The present invention relates to an improved process for preparing hydrazine and various hydrocarbyl-substituted hydrazines.
Hydrazine, alkyl-substituted hydrazines, particularly unsymmetrical dimethylhydrazine (UDMH), and phenyl-substituted hydrazines, are important commercial compounds having a wide range of utilities, such as pharmaceuticals, fuels, agricultural products, intermediates in the preparation of blowing agents, and the like.
A number of processes have been used heretofore for the preparation of hydrazine and its derivatives. For example, the Raschig process is a commercial synthesis of hydrazine from chloramine and ammonia in aqueous solution. Intially, sodium hypochlorite is reacted with an excess of ammonia to form chloramine, with sodium hydroxide being produced as a by-product. The chloramine then reacts with ammonia to form hydrazine. In the first stage of the process, chloramine is formed rapidly. However, in the second stage the reaction of chloramine with ammonia is slow and requires heat for completion. The rate of formation of the hydrazine product increases with temperature. As a side reaction, the hydrazine reacts with the starting chloramine to form ammonium chloride and nitrogen. In order to avoid an undesirably high rate of hydrazine decomposition by this undesirable side reaction, the process must be carried out at high temperatures (about 130.degree. C.) and with a large excess of ammonia (20:1 to 30:1) to minimize the reaction of hydrazine product with chloramine reactant. The desired hydrazine product is produced in relatively low concentration (generally from 1% to 3%) in the final reaction mixture, which contains a considerable amount of water, making recovery of anhydrous hydrazine from the mixture rather costly.
The Olin process (Kobe et al., Advances in Petroleum Chemistry and Refining, vol. 2, Interscience Pub. Inc., New York, N.Y., 1959, Chapter 9) is a modification of the Raschig process employing anhydrous ammonia, which is injected under pressure into an aqueous chloramine solution. Due to the heat of dilution, the temperature of the reaction mixture is raised to about 130.degree. C., the optimum temperature for the reaction of ammonia with chloramine. However, additional heat must be provided from an outside fuel source to carry the reaction to completion and to separate the relatively small concentration of hydrazine from the rather large volume of ammonia in subsequent distillation steps. Further energy is required to remove sodium chloride and sodium hydroxide by-products and to recover the hydrazine. As in the Raschig process, the hydrazine is recovered as the monohydrate. To obtain the pure anhydrous product substantial additional energy is required to drive off the chemically bound water.
The Schestakoff method is based on the degradation of urea by sodium hypochlorite to produce hydrazine. The reaction is analogous to the Hoffmann preparation of primary amines from amides. In the process, a cold aqueous solution of urea and sodium hydroxide is added to a cold aqueous solution of sodium hypochlorite. The heat of reaction increases the temperature to 100.degree. C., at which the reaction takes place at a relatively fast rate. Large quantities of steam must be used in the preparation of the urea solution (43% solution) to offset the huge endotherm of solution. The product, as in the aforementioned commercial processes, is hydrazine monohydrate in rather low concentration (about 3%). Additional energy is required to concentrate, convert the hydrate and fractionate the final hydrazine product. Excessive quantities of alkali and alkali salts are produced as by-products (ratio about 12:1 of by-products to N.sub.2 H.sub.4 thus manufactured, by weight), which are not reusable in the process.
The Bergbau or Bayer process is yet another commercial procedure for the production of hydrazine. The energy requirements of the Bergbau process are not as great as in the above-described commercial processes. In this process, ammonia is reacted with chlorine in the presence of a ketone to form an intermediate diazocyclopropane or ketazine. The intermediate is then hydrolyzed to the hydrazine hydrate and the latter converted to the desired anhydrous product. The energy requirements for recovery of the hydrazine are approximately the same as for the commercial processes previously described, which involve recovery from aqueous reaction mixtures.
It can thus be seen that the most well known and widely practiced hydrazine manufacturing processes produce a hydrate of hydrazine, which requires substantial energy for recovery of the anhydrous product.
In view of constantly rising energy costs, it is of paramount importance to minimize the use of energy in excess of thermodynamic requirements needed to complete a given reaction. In considering the overall energy requirements of any chemical manufacturing process, the energy needed for the production of raw materials and auxiliary chemicals must also be taken into accout. Thus, in the case of hydrazine, the energy requirement for providing NH.sub.3, Cl.sub.2, NaOCl, urea, NaOH etc., is a significant factor in determining the degree of gain or loss in the energy required to make the final product. Similarly, the weight ratio of by-products versus the desired end-product must be evaluated as another important factor in the overall efficiency of a process. Considered in this light, the above-described prior art methods for the production of hydrazine are decidedly inefficient, especially when it is considered that fifty-eight kcal./mole of product hydrazine are lost from the system upon the formation of hydrazine hydrate.
A process currently used for the commercial production of UDHM involves nitrosation of the sulfuric acid salt of dimethylamine using sodium nitrite to obtain dimethylnitrosamine, which is reduced to the desired product. In addition to suffering from many of the inefficiencies noted above with respect to the hydrazine processes, the dimethylnitrosamine produced as an intermedate in this process is a known carcinogen and poses a potential hazard not only to personnel operating the process but to the environment as well. Because of this potential hazard, the Occupational Safety and Health Administration (OSHA) has implemented strict rules regulating manufacturing processes in which any nitrosamine is used or produced.
Many of the inefficiencies and the hazards inherent in the prior art have been overcome by the process described in my U.S. Pat. No. 4,286,108, which produces hydrazine and hydrocarbyl-substituted hydrazines by reacting a tertiary hydrazinium halide with a compound selected from the group consisting of an alkali metal amide, an alkaline earth metal amide, a hydrocarbyl-substituted alkali metal amide or a hydrocarbyl-substituted alkaline earth metal amide, in the presence of a non-aqueous inert carrier.
One of the reactants used in the preparation of the tertiary hydrazinium halide according to the process of the 108 patent is chloramine produced by reacting ammonia gas with chlorine. A by-product of this reaction is ammonium chloride which has a tendency to clog the reactant delivery lines, and generally hampers operation of the process.